matsumoto 2012-comparisons of rapid load test, dynamic load test and static load test

Comparisons of rapid load test, dynamic load test and static load test on driven piles Bamrungwong, C., Chaisukhang, J. & Janmonta, K. Department of Rural Roa ds, Thailand Kitiyodom, P. Geotechnical & Foundation Engineering Co., Ltd., Thailand Matsumoto, T. Kanazawa Univer sity, Japan Matsuzawa, K. International Association for Spring Hammer Rapid Load Tes t, Japan Youwai, S. King Mongkut ’s University of Technology Thonburi , Thailand Keywords: rapid load test, driven pile, load-displacement relation, case study ABSTRACT: Static load test (SLT) is usually used to obtain the bearing characteristics of a pile. However, it requires relatively high cost and testing period. In contrast, rapid load testing requires less cost and testing period. As one of rapid load test methods, Spring Hammer (SH, hereafter) rapid load test method has been developed in Japan. In this paper, validity of the SH test method with a simplified signal interpretation to estimate the static behaviour of a pile is discussed and demonstrated through comparison of the results from SLT and the SH test, as well as the results from dynamic load test (DLT). 1 INTRODUCTION In Thailand, static load test (SLT) or dynamic load test (DLT) is employed to obtain the bearing characteristics of a pile. Due to the lack of capable dynamic load test result interpreter, it is widely believed that static load test is the most reliable method to obtain the load-settlement behaviour of a pile. However, static load test requires high cost and testing period. Therefore, pile design has been mainly based on empirical equations and soil information from borehole investigation without any load test by adopting excessive design requirements, i.e. high factor of safety. In order to overcome the above situation, rapid load test methods have been proposed. As one of rapid load test methods, the Spring Hammer test (SH test) was developed in Japan (Matsumoto et al., 2004). Loading mechanism of the SH test is basically similar to Dynatest (Gonin & Leonard, 1984) Statnamic test (Bermingham & Janes, 1989) and Pseudo-static test (Schellingerhout & Revoort, 1996). In the SH test method, the simple non-linear damping interpretation method (Matsumoto et al., 1994) is usually used to derive static load-settlement curve. In this paper, in order to verify the applicability of the SH test in Thailand. SH tests were conducted on driven concrete piles at five DRR (Dept. of Rural Roads) bridge construction sites in Thailand. The validity of the SH test method to estimate the static behaviour of a pile is examined through comparison of the results from SLT, DLT and the SH test. 2 SPRING HAMMER TEST METHOD Several SH test devices are available, although their loading mechanism and measuring system are the same in the devices. Figure 1 shows the loading system and the measurement system of the SH test. Figure 2 shows a SH test device used in this work. A spring unit is mounted on the leader mast of pile driving rig to prevent deviations of the central axis of pile, spring unit and hammer. Maximum load capacity is 2500 kN when using a hammer mass of 9.3 ton and a falling height of 1 m, which ensures confirmation of static pile capacity at least 2000 kN A load cell is placed on the pile top directly, on which the spring unit is placed. A hammer mass is dropped onto the spring unit to provide impact loading on the pile top. The acceleration at the pile top is measured using two accelerometers. The pile top displacement is measured by means of a laser or an optical displacement transducer. The dynamic signals are sampled at a sampling frequency greater than 1 kHz. The output dynamic signals are recorded through a computerised data acquisition system. The recorded dynamic signals are promptly processed to derive ‘static’ response of the pile using the Non-Linear Damping method. The spring unit consists of a number of coned disc springs. The total spring stiffness of the spring unit is easily controlled by changing arrangement of the coned disc springs. The maximum load and loading duration can be widely varied by changing combination of the spring stiffness, the hammer mass and the falling height of hammer. 795

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